1. Field
Various embodiments of the present invention relate to semiconductor device fabrication technology and, more particularly, to an image sensor having pixels capable of detecting phase differences.
2. Description of the Related Art
Most imaging devices, such as digital cameras and camcorders, adopt auto-focus systems. Auto-focus systems are divided into those that use a phase difference detecting scheme and those that use a contrast detecting scheme.
Phase difference auto-focus systems have a sensor for detecting phase differences in addition to an image sensor. Auto-focusing is accomplished by adjusting the lens based on an output of the phase difference detecting sensor. The phase difference auto-focus detecting scheme also requires a mirror. For example, in an auto-focusing scheme for a Digital Single Lens Reflection (DSLR) camera, a sub-mirror for guiding incident light into the phase difference detecting sensor is provided in addition to a main mirror. The phase difference-based auto-focusing is advantageous in that fast-high-performance auto-focusing is possible. However, the phase difference-based auto-focusing is a high-cost system since it requires both a sensor dedicated to phase difference-based auto-focusing, and an optical system.
In comparison, contrast detecting scheme auto-focus systems rely on high-frequency data from the image sensor. This method of auto-focusing is referred to as a contrast auto-focusing. Since contrast auto-focusing does not require the signal processing circuit and the additional sensor, which are essential in phase difference-based auto-focusing, contrast auto-focusing has a relatively low cost. However, contrast auto-focusing is slower and less accurate than phase difference-based auto-focusing.